The present invention relates to multi-piece solid golf balls having a core, at least one mantle layer, and a cover.
Golf balls in which a soft cover serves as the outermost layer have been proposed to meet the requirements of professional golfers and skilled amateurs (see, for example, JP-A 6-343718, JP-A 7-194736, JP-A 7-24085 and JP-A 9-239068).
In such golf balls, the outermost layer which comes into contact with the golf club is generally an ionomer cover. A desire has thus existed for further improvement in scuff resistance to shots made with a short iron or a wedge.
Moreover, there is a widespread desire among golfers for balls which, in addition to being endowed with better scuff resistance, also have good resistance to cracking with repeated impact, a good feel upon impact, and good spin stability.
It is therefore an object of the invention to provide golf balls which, even when used by ordinary golfers having amateur-level head speeds, provide a good balance between the flight characteristics, controllability, spin stability, feel, scuff resistance and durability to repeated impact.
We have found that multi-piece solid golf balls which are composed of a core, at least one mantle layer enclosing the core, and a cover that is made of a thermoplastic polyurethane composition, in which the average hardness of the core, the cover hardness, the difference between the cover hardness and the mantle layer hardness, and the difference between the outermost layer hardness and the average core hardness have each been optimized, and which have been imparted with a high initial velocity exhibit a good balance between the flight characteristics, controllability, spin stability, feel upon impact, scuff resistance and durability to repeated impact, even when used by golfers having a head speed of about 40 m/s or less.
Accordingly, the invention provides the following golf balls.
(I) A multi-piece solid golf ball having a core, at least one mantle layer enclosing the core, and a cover; wherein the cover is made primarily of a thermoplastic polyurethane composition, the cover and the mantle layer have a difference in Shore D hardness therebetween such that xe2x88x928xe2x89xa6[(cover hardness)xe2x88x92(mantle layer hardness)]xe2x89xa65, the cover and the core have a difference in Shore D hardness therebetween such that 5xe2x89xa6[(cover hardness)xe2x88x92(average core hardness)]xe2x89xa625, the core has an average Shore D hardness of 30 to 50, the cover has a Shore D hardness of at least 52, and the ball has an initial velocity of at least 76.4 m/s.
(II) The multi-piece solid golf ball of (I) above, wherein the core is made of an organosulfur compound-containing rubber composition.
(III) The multi-piece solid golf ball of (I) above, wherein the difference in Shore D hardness between the cover and the mantle layer is such that xe2x88x923xe2x89xa6[(cover hardness)xe2x88x92(mantle layer hardness)]xe2x89xa63.
(IV) The multi-piece solid golf ball of (I) above, wherein the cover and the core have a difference in Shore D hardness therebetween such that 15xe2x89xa6[(cover hardness)xe2x88x92(core center hardness)]xe2x89xa625.
(V) The multi-piece solid golf ball of (I) above, wherein the core has an average Shore D hardness of 35 to 45.
(VI) The multi-piece solid golf ball of (I) above, wherein the thermoplastic polyurethane composition includes (A) a thermoplastic polyurethane and (B) an isocyanate mixture prepared by dispersing (b-1) a compound having as functional groups at least two isocyanate groups per molecule in (b-2) a thermoplastic resin that is substantially non-reactive with isocyanate.
(VII) The multi-piece solid golf ball of (I) above, wherein the mantle layer is composed primarily of a mixture prepared from a base resin of
(C) an ionomer resin component containing
(c-1) an olefin/unsaturated carboxylic acid random bipolymer and/or a metal ion neutralization product of an olefin/unsaturated carboxylic acid random bipolymer, and
(c-2) an olefin/unsaturated carboxylic acid/unsaturated carboxylic acid ester random terpolymer and/or a metal ion neutralization product of an olefin/unsaturated carboxylic acid/unsaturated carboxylic acid ester random terpolymer in a weight ratio (c-1)/(c-2) of 100/0 to 25/75, and
(D) a non-ionomer thermoplastic elastomer in a weight ratio C/D of 100/0 to 50/50, to which base resin is added:
(E) a fatty acid having a molecular weight of 280 to 1,500 or a derivative thereof, and
(F) a basic metal compound such as to satisfy the respective weight ratios (C+D)/E=100/5 to 100/80 and (C+D)/F=100/0.1 to 100/10.
(VIII) The multi-piece solid golf ball of (VII) above, wherein the non-ionomer thermoplastic elastomer (D) is an olefin thermoplastic elastomer containing crystalline polyethylene blocks as hard segments.